Examples of driver assistance systems in which the present invention is used are, for example, so-called ACC systems (adaptive cruise control), which allow an automatic regulation of the distance to a preceding vehicle (the object), as well as predictive safety systems (PSS), which are used for automatically recognizing an imminent collision, so that measures for avoiding the collision or for mitigating the collision consequences may be initiated.
Precise knowledge of the lateral movements of the object is significant, for example, in the cases in which a merging vehicle, from which an increased danger of collision originates, is to be recognized as early as possible or, vice versa, the earliest possible recognition of vehicles turning off or leaving the host vehicle's lane is necessary, so that the host vehicle is not decelerated unnecessarily strongly and/or may accelerate again earlier.
The transverse component of the velocity (in the direction transverse to the roadway) and the yaw rate of the object may be cited in particular as examples of dynamic variables which are representative for the lateral movement of an object. The yaw rate is significant because it allows an early estimation of the future movement direction and thus the lateral velocity of the object.
Typical driver assistance systems normally have an angle-resolving, long-range radar sensor (LRR) for locating preceding vehicles and other objects, using which the distance and the relative velocity or, more precisely, the radial component of the relative velocity may be measured relatively precisely. The angle resolution capability of the radar sensor additionally allows at least a coarse estimation of the azimuth angle, so that together with the distance information, the position of the object in a two-dimensional coordinate system may be determined. Because of the limited angle resolution capability, the precision when determining the lateral position (y position) of the object is significantly worse, however, than the precision when determining the distance.
A direct measurement of the transverse component of the velocity of the object is not possible. This variable may therefore only be determined indirectly, by tracking the lateral positions of the object over a certain period of time and differentiating with respect to time. The unavoidable inaccuracies in the measurement of the lateral position of the object are reinforced still further upon the calculation of the derivatives with respect to time, so that the results are subject to significant measurement noise, which may not be entirely suppressed even by filtering the data. The calculation of the derivative with respect to time and the filtering operations additionally have the result that the data for the lateral velocity of the object are only available comparatively late.
A driver assistance system is described in German Patent No. DE 199 49 409, in which two short-range radar sensors (SRR) are used for locating objects ahead of the vehicle, which only measure distances and relative velocities, but not azimuth angle. Because the two sensors are situated laterally offset to one another, however, the lateral position of the object may be determined at least approximately by triangulation on the basis of the distance data. The lateral velocity may also only be determined here by differentiation with respect to time.
German Patent No. DE 10 2004 028 822 describes a driver assistance system having a “scanning” distance sensor, such as a radar or lidar sensor, using which the rear of a preceding vehicle may be scanned, so that distance data are obtained for multiple points on the rear of the object, the particular associated azimuth angles being known. Under the assumption that the reflection points from which the distance data are obtained lie approximately on a straight line which is oriented perpendicular to the longitudinal axis and thus to the motion direction of the object, the orientation of the object and, on the basis of this, the lateral velocity of the object are determined from the distance data. The precision is also decisively a function of the angle resolution capability of the sensor in this method.